Cylindrical spray holes are usually provided in fuel injectors currently in use for direct gasoline injection for preparing the fuel mixture. Stepped spray holes are currently used to protect the spray hole from deposits and to achieve a shortening of the spray hole at a constant spray hole disk thickness.
Patent document WO 02/084104 A1 discusses a fuel injector for fuel injection systems of internal combustion engines, which includes a magnet coil, a valve needle that is operatively connected to the magnet coil and is acted upon in the closing direction by a restoring spring for operating a valve closing body, which forms a sealing seat together with a valve seat face formed on a valve seat body, and at least two spray discharge openings formed in the valve seat body. The spray discharge openings are formed in the valve seat body in such a way that they are shielded from the circulating flows of mixture in a combustion chamber of the internal combustion engine and therefore have a cylindrical spray discharge hole and a ring wall adjacent thereto, the latter wall being high enough to shield each of the spray discharge openings from the flows circulating in the combustion chamber.
To achieve an increase in spray angle, it is also known in the related art that the length/diameter ratio of the spray hole may be reduced, but the reduction in length of the spray hole is limited due to the associated decline in strength of the spray hole disk.
In addition, for manifold injection, valves having trumpet-shaped spray holes are used, imparting a high transverse movement to the stream already within the spray hole and thereby allowing rapid and good atomization. This also achieves an increase in the spray angle, but with moderate stream stability. With such a configuration, the stream angle depends greatly on the oncoming flow ratios.
With the valves described above, there is the disadvantage that the mixture is processed via a turbulent, approximately cylindrical free jet having a relatively low surface/volume ratio.
Furthermore, valves for low-pressure spraying, having conical spray holes at a great inclination, are also known. Since the mass spray-discharged as a thin film atomizes much better than the main jet, there is an improvement in SMD on the whole, but this geometry is not suitable for fuel injectors having stepped spray holes, and the cross-flow, which is created primarily by angle φ of inclination of the spray hole, is necessarily coupled to spray discharge angle γ.